Hi Tech, can you throw some light here.
i drove home and noticed for first time the radiator over flow bottle was gargling and bubbling quite noticeably.

I let it cool down and next day checked and found the suspect might be a bad Radiator cap, the engine oil is clean and the exhaust is normal. Nothing smells out of the ordinary or any leaks. I topped up the plastic overflow bottle with few ounces of coolant and will replace cap. The temperature gauge is normal reading after 30km driving and does not show over heating normally.
Any tips or reasons why this may boil and gargle?
Thanks

 

Chances are your theory is correct. See what happens with the new cap. It could be that you have gotten some air in the system. After a few warm-up and cool-down cycles, the air should work its own way out and you may need to top up again. Whatever you do, DON'T touch the bleed screw on the plastic manifold on top of the engine to bleed air. You will almost certainly strip out the bleed screw seat from the plastic body of the manifold and wind up having to replace it.

 

Thanks Dcotter for your reply. I will change the Radiator cap today and see what happens. As for that bleed screw, i know exactly what you mean. Its just for show as i could not open it without fear of breaking it when i replaced the black housing TWICE already.

 

The bleed screw is not "just for show". They used it in the factory when they first filled the system with coolant. It was necessary then to avoid trapping air in the system. The problem is that after it has been screwed closed for a year or two, the bleed screw will seize to the threads of the insert, and if you try to unscrew it, the insert will spin in the plastic housing, stripping it out and causing a leak. Aftermarket housings have a re-designed insert that you can hold with a wrench to prevent turning it. The home mechanic can simply avoid ever touching the bleed screw by letting the system bleed itself and topping up after a few trips, as pointed out above. You are not the only one to have learned about that bleed screw the hard way. This has been written up here on the forum several times in the hope that it might prevent at least a few people from having to suffer through the consequences.

 

Hi Thanks for the background on bleed screw. I have been following your tips for a few years now and learnt a lot.
even on brand new housings i have installed, and i installed two, both had bleed screws that did not look like they were going to budge. However there are several more expensive ones, that might be better for that.
Today i am installing the rear rubber brake hose and over hauling the caliper on 2006 Sebring Touring 2.7L.
Many thanks.

 

Sound like coffee percolating? if so the science behind that is when the engine is running it makes pressure like a tea pot. When cooling off it makes a vacuum.
SO when you turn the engine off the coolant is no long flowing around and the spring or seal on the Radiator cap is weak and will will allow the coolant to bubble out in the over flow tank sounds like coffee..